1. Technical Field
The present disclosure relates, in general, to a filter, a method of making a filter and a method of filtering a fluid.
More particularly, the present disclosure relates to a filter having alternating layers of non-filtering diffusion medium and filter medium. Some of the layers of the filter medium are provided with bypass apertures, while the remaining layers do not include bypass apertures so that they act as qualifying layers for the filter. Filters according to the present disclosure have been found to provide improved fluid distribution over the filter medium, reduced pressure drop and increased filter life, without a reduction in filter rating.
2. Discussion of Background Disclosures
In general, a filter assembly is used for removing contaminants from fluids, i.e., liquids or gases. Such filter assemblies, for example, are used in chemical and hydrocarbon applications such as polyethylene manufacturing, food and beverage applications, electronic applications such as circuit board construction, coating applications such as high quality spray painting, and industrial applications such as paper manufacturing. Many filter assemblies include a tubular filter cartridge contained in a filter housing. The filter housing includes a sump, wherein the filter cartridge sits, and a head sealing the filter cartridge within the sump such that the housing acts as a fluid-tight pressure vessel. The filter head includes an inlet between the sump and the filter cartridge, and an outlet aligned with the tubular filter cartridge. Contaminated fluid is pumped into the filter housing through the inlet, and radially inwardly through the filter cartridge to produce filtered fluid, which then exits the filter housing through the outlet.
Normally, such a filter cartridge includes an elongated, tubular, perforated core wrapped with layers of depth filter medium. A typical depth filter medium is a non-woven, porous, melt-blown sheet or sheets of polypropylene micro fibers. The depth filter medium can have a uniform pore structure or a graded or tapered pore structure, whereby the pore size of the depth filter medium decreases in the direction of fluid flow, i.e. from an outer to an inner diameter of the filter. The depth filter medium can also be provided with fibers of varying diameter.
Even with a tapered pore structure and/or varying fiber diameters, however, it has been found that many depth filters actually act as xe2x80x9clow areaxe2x80x9d surface filters, since only one or two of the multiple layers of filter medium within the depth are heavily loaded and plugged with contaminants after use, while the remaining layers are relatively clean (it should be noted that these are general observations, as the performance of a particular filter can depend on the particle size and distribution of contaminants in a fluid to be filtered). When a depth filter cartridge mimics a surface filter and collects contaminants in primarily one layer, the results are an inefficient distribution of fluid over the filter medium, a higher pressure drop for fluid passing through the filter and a lower flow rate capability for the filter. Such filters also tend to have a shorter useful life, and thus must be replaced more often.
A variety of depth filter cartridge configurations have been proposed and/or utilized over the years in efforts to provide improved performance. For example, U.S. Pat. No. 4,863,602 to Johnson shows a filter element that includes a plurality of layers of flexible, fluid permeable filtering material, at least one layer of which includes an opening through which fluid may pass, a layer of flexible, fluid-permeable, substantially nonfiltering transport material, and a layer of flexible prefiltering material positioned upstream of the plurality of layers of filtering material to xe2x80x9cfilter out from the fluid substantially all particles that could otherwise become lodged in the transport material but not to filter out significantly smaller particles.xe2x80x9d
U.S. Pat. Nos. 5,174,895 and 5,015,379 to Drori disclose filter elements featuring at least one coiled filter strip defining first and second butt ends. The Drori filter elements fail to optimally enhance fluid flow while providing extended filter service life. Additional filter designs of background interest are disclosed in U.S. Pat. No. 4,877,526 to Johnson; U.S. Pat. No. 4,882,056 to Degen et al.; U.S. Pat. No. 5,468,382 to Cook et al.; and U.S. Pat. No. 5,591,335 to Barboza et al.
Despite the various configurations known in the art, however, there remains a need for a filter cartridge providing improved distribution of fluid over the filter medium therein, a lower pressure drop and long useful life, without reducing the filter rating and that is economical to manufacture and utilize.
A filter for filtering contaminated fluid is disclosed herein. A preferred filter includes alternating layers of a filter medium and a diffusion medium, with at least a portion of the layers of the filter medium having bypass apertures and acting as pre-qualifying filter medium layer(s).
The diffusion medium includes a first plane of spaced-apart, substantially parallel strands defining first longitudinal passages. The longitudinal passages have a height dimension and a width dimension. The diffusion medium further includes a second plane of spaced-apart, substantially parallel strands defining second longitudinal passages. The second longitudinal passages also define a height dimension and a width dimension. The diffusion medium""s second plane of strands are oriented in a non-parallel manner with respect to the strands of the first plane such that the first and the second planes define lateral openings. Those lateral openings define side dimensions. The first and the second longitudinal passages are sized such that at least one dimension is smaller than any of the side dimensions of the lateral openings.
Filters of the type disclosed herein demonstrate superior fluid distribution over the filter medium contained therein, and an optimum use of the filter medium. Filters according to the present disclosure, therefore, have an increased life and a lower pressure drop without a reduction in filter rating, and provide more cost effective filtering.
The filters of the present disclosure may be used in methods to filter contaminated fluids in a wide range of commercial applications. Such filters and filtration methods are described in greater detail hereinbelow.